A heater used in, for example, a glow plug of an automobile engine includes an insulating base and an electrically conductive line embedded in the insulating base. The electrically conductive line includes a resistor including a heat-generating portion and a lead led out at the surface of the insulating base. The lead is designed or the material of the lead is selected so that the lead has a lower resistance than the resistor (see, for example, PTL 1).